(1) Field of the Invention
This invention relates to an oscillation circuit which comprises a few switching transistors and loads in its amplifier portion and a capacitive element. More particularly, it provides an oscillation circuit in which switching elements and loads in the amplifier portion are constructed in the form of integrated injection logic (I.sup.2 L) circuits, whereby the oscillation circuit requires only a very small area in a semiconductor integrated circuit (IC), exhibits a high performance and is capable of a low voltage operation (at approximately 0.6 V) as well as a low power operation.
(2) Description of the Prior Art
Various systems often require timing clocks, clocks for the analog-to-digital conversion, clocks for time-keeping devices, etc. In order to generate such clocks, an oscillation circuit is needed.
Especially in a case where a system is constructed by the use of an integrated circuit, it is desirable that the oscillation circuit can be formed on an identical chip together with the other circuits. In that case, it is desired that the oscillation circuit can be realized in the smallest possible area.
Also in a case where a system is constructed by the use of an integrated injection logic circuit, the oscillation circuit is often necessary. Heretofore, in the case of assembling the oscillation circuit into the system employing the I.sup.2 L circuit, the oscillation circuit has often been formed of ordinary transistors and resistors by exploiting the fact that the I.sup.2 L circuit and the other circuits such as linear circuits can coexist on an identical chip. In this case, although the oscillation circuit can coexist on the identical chip, its occupying area becomes very large on account of the use of the usual transistors, resistors etc. Another difficulty is that the oscillation output needs to be converted up to the operating voltage level of the I.sup.2 L circuit.
As a circuit improved in the above points, there has been proposed an oscillation circuit as shown in FIG. 1 wherein an integrated injection logic circuit and ordinary transistors mix ("Denshi Tsushin Gakkai, Gijutsu Kenkyu Hokoku"--Technical Research Report of the Electronics and Communication Society--, Vol. 75, No. 209, SSD75-67 to 72, pp. 41-50, published Jan. 27, 1976). The circuit of FIG. 1 has such merits that no resistors are required, that the number of constituent elemens of the oscillation circuit is small, and that the conversion of the output voltage level for the I.sup.2 L circuit is unnecessary. Since, however, the ordinary elements such as npn and pnp transistors and diodes are employed, the areas of these elements are large, and the oscillation circuit still occupies a large area.